The two main contenders are the single-degenerate (SD), and the
double-degenerate (DD) scenarios. In the SD scenario, a CO white dwarf accretes
material from a non-degenerate companion. If the white dwarf has a mass close to
the Chandrasekhar limit (\(\approx 1.38\)  \(\textrm {M}_{\odot }\) , hereafter referred to as M\(_{\textrm {Ch}}\) ),
accretion causes the central temperature to rise until oxygen burning is
triggered [1]}, [2]}. If on the other hand the white
dwarf has a mass significantly below M\(_{\textrm {Ch}}\) , a detonation can be triggered on the
surface of the white dwarf if the accreting material is He. Under specific
circumstances a shock wave can then propagate to the centre of the white dwarf
and detonate it (an “edge-lit” “double detonation”) [3]}. In the
DD scenario, two white dwarfs in a close orbit around each other merge after
radiating gravity waves [4]}, [5]}, and the resulting
massive white dwarf explodes, leaving no remnant, if it avoids accretion-induced
collapse [6]}. Explosion is more likely if the merging occurs
“violently” [7]}. Recently, two more scenarios have been proposed.
The head-on collision of two white dwarfs, possibly aided by a third body in a
triple system, is a variation of the DD scenario which may lead to explosion and
the creation of two distinct ejecta [8]}, [9]}. This scenario
has specific observational consequences [10]}. Finally, the explosion
of a white dwarf engulfed in a common envelope by the outer layers of an
asymptotic giant branch (AGB) star and merging with the AGB star's degenerate
core, the “core-degenerate” scenario, has also been proposed as a channel to
produce SNe Ia [11]}, [12]}, [13]}.
[14]} review possible progenitor/exposion channels.
